Isocyanates account for the highest number of reported cases of occupational asthma in the U.S. and other developed countries. However, primary prevention is limited by inadequate knowledge of isocyanate exposure patterns and the factors which both cause and exacerbate the disease. Secondary and tertiary prevention opportunities are limited since there is currently no simple way to diagnose isocyanate asthma, or identify at-risk groups. To address these important problems, the investigators propose an epidemiologic study of HDI-exposed auto-body shop spray painters and co-workers. The specific aims are to: 1) Develop an algorithm for the diagnosis of isocyanate asthma using widely available questionnaire and physiologic measures validated against specific bronchial challenge; 2) Characterize isocyanate exposure patterns in auto-body shops to determine the relationships between exposures and risk for development and progression of isocyanate asthma; and 3) Identify potential acquired and genetic host susceptibility factors which may modify risk for the disease. The overall study design will be a cross-sectional investigation of fifty shops with 300 workers. When clinical, environmental, and host-modifying factors are fully evaluated, this project should result in the highly practical knowledge needed to diagnose and prevent this important occupational disease.